Congratulations on your USC and Stern Admits!
If you are set on IB, Stern, Columbia, or Darden are the schools for that recruiting path. Most IB happens in New York and there is no way around it. You may luck out at USC and connect with an alum in New York (there are likely some Boutique IB firms in LA but they will be fairly small is my guess and it is only a guess). East Coasters do not give a lot of credit to any West Coast school except Stanford and the impression is that you will be late, likely show up in shorts, and you have surfed through most of your classes... at least that was the impression a few years ago.
I think you can make it work if you are OK being in LA and working in a small boutique firm. If you want a shot at the better opportunities in New York and top firms, you have to go to Stern. You should try to validate this decision with the finance clubs at both programs and see what they are doing for IB recruiting and how chances look for international applicants (it is a diff game for domestic vs. international since not all hire H1B's).
P.S. Here is one idea - do you have an ability to network and connect with a potential IB contact in the US to do a virtual coffee chat or skype? This would be an informational interview that should be pretty safe and potentially ask them about what choice they would recommend making. This would be very safe for them since you would not ask for a job for at least 2 years and would not be bugging them for an internship for at least 6 (and they could not promise you anything anwway with the COVID19 handing in New York air) but it is a perfect opportunity to ask people where you should go and get a jump start on your networking and your career. This would potentially give you a perfect excuse to reach out in the fall about an internship
People are bored and it could be a fun puzzle that someone on LinkedIn may just reply to.